Can bat guano make you sick?

In larger quantities, the ammonia given off by bat guano can be toxic to humans. Bats can also carry some pathogens that can pass into their feces that might be a problem. BUT, if the guano is dried or dessicated, it is not likely to be too much of a problem. There can be smells and dust, but if you are talking about a small infestation in a home or outbuilding, just clean it up and there should be no problem.